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5. Other Determinations.—The temperature of inflammability and
the viscosity may also be required; these are ascertained as with heavy
mineral oils (see these: Chapter VIII).

* *

The composition of impregnating oils varies according to the conditions of
the contract. Thus, a specific gravity of I-03-1-10 or of 1-05 at 50° is required :
a content of 5-30% of naphthalene ; a content in phenols of 5-10%, and various
boning points.1


Commercial benzoles from the tar industry are mixtures in varying
proportions of benzene, toluene and xylenes, and contain also ethylbenzene,
trimethylbenzenes and other homologues of benzene. The separate pure
hydrocarbons are obtained by
further and complicated rectifica-

The rectified benzoles are colour-
less, limpid liquids with a character-
istic, pleasant odour ; any turbidity
indicates presence of water.

The tests and determinations to
be made are :

1.     Determination     of     the
Specific  Gravity.—By the   West-
phal balance, densimeter or picno-

2.   Distillation. — This    test,
which   serves to characterise com-
mercial   benzoles,   may  be  carried
out in an ordinary distillation flask,
similar to that used for light mineral
oils.     Industrially, however, the de-
tailed instructions   given by Krae-
mer and Spilker2 are   followed, so
that   comparable   results   may   be

FIG. 37


The distillation apparatus used is
represented in Fig. 37 and consists of a copper vessel A, 0-6-0-7 mm. thick,
about 150 c.c. in capacity and of the dimensions indicated. To the mouth
of the vessel is fitted a dephlegmator B, 14 mm. wide and 150 mm. long,
furnished with a bulb and with a side-tube, 8 mm. in diameter, fixed almost
at right angles. A thermometer, reading to 0-1° or 0-05° (for'commercial
benzoles) is introduced so that its bulb is in the centre of the bulb.

1  For greater details, see Lunge :  Coal-Tar and Ammonia (London, 1916), p. 695 ;
Allen :   Commercial Organic Analysis, 4th. edit., 1910, Vol. Ill, p. 368.

2  Muspratt:  Chemie, 4th edit., 1905, Vol. VIII, p. 34.hich is heated so that 120 drops per minute pass